This paper explores the implications of an increasing reliance on project forms for learning within organizations. In particular, we focus on the tensions between learning at project level and the stocks and flows of organizational knowledge. Based on a review of the existing literature, we outline propositions on two major processes of project-based learning (PBL): ‘learning-by-absorption’ and ‘learning-by-reflection’. Subsequently, the paper applies and refines this framework through the analysis of the findings from a qualitative study of three linked projects in the UK water industry. The findings from our study support and highlight the role of the above-noted processes in determining the extent and transfer of PBL. In particular, they indicate the role played by ‘quasi-organizational’ forms in enabling ‘learning-by-absorption’ and ‘learning-by-reflection’ at a project level. But equally, they help to explain limitations on the ability of project-based learning to bring about significant changes in knowledge stocks and flows in the wider organization.